The invention relates to a power tool comprising a motor which is couplable to a drive, an energy supply device for the provision of electric energy, a controller having a motor controller for activating the motor, and further comprising an operating-state recognition module which is configured to detect at least one operating-state variable and, as a function of this, to output a brake signal.
The subject of the invention is, furthermore, a method for decelerating a drive movement of a power tool.
A power tool of this type is known from DE 10 2008 033 866 A1.
The known power tool is a machine tool with a controller having a limitation device for limiting an output torque provided on the drive side. The controller is designed for activating, as a function of at least one brake condition, a current feed device in a brake operating mode in which a motor from the machine tool is braked by means of a contradirectional rotating field.
Power tools with electric motors are employed in many fields of use. Thus, inter alia, many diverse appliances and machines are known for drilling, screwing, percussion drilling, sawing, cutting, grinding or polishing.
Conventionally, the power tools have a drive train with an electric motor, a tool-holding fixture, drivable by the motor, for receiving a tool, and also, if required, an interposed transmission device. The motors used are, in the case of high-performance power tools, heavy-duty motors with a low power/weight ratio or high power density. Motors of this type have, for example, nominal rotational speeds of approximately 10 000 min−1 to 30 000 min−1.
With regard to the transmission device and to a tool which may possibly have a high moment of inertia, during operation at high rotational speeds states may arise in which the drive train of the power tool has high kinetic energy. In specific operating states, it is desirable to reduce this energy as quickly as possible so that as rapid a tool standstill as possible or at least deceleration can be brought about. These states may, for example, be those which are dependent on the work progress, for example on reaching a desired depth in the case of a screwing or drilling action or on reaching a desired tightening torque in a screwing action. However, rapid deceleration may also be necessary when an inadmissible operating state is recognized, for example excessive twisting of the power tool on account of a high moment of reaction if the tool is jammed A decelerating action may also serve for quickly braking a tool taking relatively long to slow down, for example an angle grinder, for example in order to put it down safely immediately after use.
In DE 2008 033 866 A1, it is proposed, for the purpose of limiting the output torque of a machine tool, to act upon the motor of the latter with a rotating field contradirectional to the instantaneous direction of rotation. By means of a brake operating mode initiated in this way, the output torque of the machine tool is to be regulated.
It has been shown that a feed of countercurrent to the motor can contribute to braking the power tool smoothly. However, especially in applications where high deceleration or high dynamics in regulating the braking action is desired, the feed of countercurrent may entail high loads upon components.